Best way to write lingq for loop queries - asp.net

Question

I am using oracleDB and i have view like below which contains employees and his managers.
empNo
FirstName
LastName
Manager
I need to select a person and all of his staff. IE
Person1 is Manager
-- Person1_1
----Person1_1_1
----Person1_1_2
-- Person1_1
When i login with the user of Person1, I need to get all of the persons above.
Here is my LINQ but it is too slow.. What is the efficient way to get the data ?
List<decimal> OrgPerson2 = new List<decimal>();
public List<decimal> getOrgPerson(decimal empNo)
{
List<decimal> OrgPerson = new List<decimal>();
OrgPerson.AddRange(db.CRM_PERSON_TITLE_V.Where(c => c.MANAGER == empNo).Select(c => (decimal)c.PERSONID).ToList());
var subPerson = db.CRM_PERSON_TITLE_V.ToList();
foreach (var item in OrgPerson)
{
OrgPerson2.Add(item);
var subPerson2 = subPerson.Where(c => c.MANAGER == item).Select(c => (decimal)c.PERSONID).ToList();
if (subPerson2 != null)
{
if (subPerson2.Count > 0)
{
getOrgPerson(item);
}
}
}
return OrgPerson2.Distinct().ToList();
}

Answer 1

Decided to try out your solution and as I suspected it threw a StackOverflowException for me. Recursive methods are pretty bad if you are not careful.
Here's my solution with a stack. The code is self-explanatory.
List<decimal> GetOrgPerson(decimal id)
{
Stack<Person> iter = new Stack<Person>();
List<decimal> result = new List<decimal>();
iter.Push(db.People.FirstOrDefault(p => p.ID == id));
while (iter.Count() > 0)
{
Person current = iter.Pop();
var subordinates = db.People.Where(p => p.ManagerID == current.ID);
foreach (var s in subordinates)
{
if (result.Contains(s.ID))
continue;
iter.Push(s);
result.Add(s.ID);
}
}
return result;
}
In my test-case People inherits IEnumerable interface.

Answer 2

Your query is just getting all the staff under a manager recursively, it can be greatly simplified:
public IEmunerable<decimal> getOrgPerson(decimal empNo)
{
foreach (var subEmpNo in db.CRM_PERSON_TITLE_V.Where(c => c.MANAGER == empNo).Select(c => (decimal)c.PERSONID))
{
yield return subEmpNo;
foreach (var subSubEmpNo in getOrgPerson(subEmpNo))
yield return subSubEmpNo;
}
}
You should not need Distinct() since each employee has only one manager.
Also, I assume you don't need a List<decimal> which you can add/remove items. Otherwise, you may need something like OrgPerson2 = getOrgPerson(empNo).ToList()